The study was performed at Harran University in Sanliurfa, Turkey. 100 patients over 60 y.o. who were getting a radial art line in the ICU or OR were enrolled. About 2/3 were male: mean age ~ late 60s. Exclusion criteria: peripheral vascular disease, prior hand or wrist surgery, hemorrhagic shock, morbid obesity, and patients with a tortuous artery that was difficult to image. Randomized to one of 5 groups with respect to degrees of wrist extension: 0, 15, 30, 45, 60. 20 patients per group. Two of the authors did all of the ultrasounds and art lines. Art lines were placed with the artery imaged in long axis; short axis not used. Wrist boards were prepared at these angles in advance. The angle was verified with a goniometer or similar device once the patient’s arm was placed on the board.

The height of the radial artery was greatest at 45 degrees (mean: 3.54 mm). The distance from skin to artery was the least at 45 and 60 degrees (~ 2.3 mm). First attempt success rate was best at 45 degrees, 100% vs. ~ 70-75% at other angles. Mean cannulation time was also best at 45 degrees (~ 25 seconds vs. ~ 35 seconds). All of the above reached significance. Mean number of attempts also correlated with arterial height and depth: smaller and deeper is bad. The latter is consistent with the central line and peripheral IV lit. Bigger, more superficial vessels are easier to hit.

Some issues with the study: only 2 authors performed the art lines; exclusion criteria; cannulation taking 8 seconds longer not clinically significant; also, not sure why the artery would get bigger as one goes from zero to 45 degrees of extension.

Bottom line: when placing a radial art line with POCUS, best choice would seem to be to place the wrist in 45 degrees of extension

Note: At the EDE 2 course and in the book, we focus a bit more on the transverse plane. See the vids for a radial art line in long, both without and with color Doppler. Sometimes the neighboring soft tissue can seem dark and mimic an artery. Color will help confirm that a black tube is the radial artery and not hypoechoic soft tissue.